A. Field of the Invention
The present invention relates to programming microcontroller-based systems, and more particularly, relates to utilizing the synchronous serial port of an energy meter microcontroller for asynchronous communication so as to increase the rate of re-programming.
B. Related Art
With respect to the energy metering art, the advantages of asynchronous communications over synchronous communications are well known. In addition, the cost to add hardware for asynchronous communications ability to a microcontroller initially having only synchronous communication ability typically are high as compared to the overall cost of an energy meter. Providing the advantages of asynchronous communication without such hardware costs is desirable.
In addition, with respect to the energy metering art, reducing the amount of time to re-program meter registers is highly desirable. Particularly, the meter reader who re-programs a meter register in the field will have lower productivity if re-programming meter registers requires a greater amount of time. Also, temporary accumulators are required to hold energy consumption information acquired during programming but which information cannot be processed until the programming has been completed. As the amount of time required to re-program increases, the necessary size of the accumulators also increases. Moreover, the accumulators occupy memory space that could otherwise be used for providing other features. If the temporary accumulators become too large, an external memory may have to be added. External memory adds more costs to the meter.
Known art includes GE's TM900 register which utilizes an NEC 75312 processor in conjunction with a synchronous optical communication protocol. With respect to programming time, and by way of example, the time required to transmit security code in such register during reprogramming is about 1.33 seconds. For registers with universal asynchronous receivers/transmitters (UARTS), such as GE's Phase3 register, security code transmission requires only 0.01 seconds. UARTS, however, add cost to the register.
It is also known to utilize a synchronous serial port for asynchronous communications in a low cost processor utilized in electronic metering applications. An example of such a scheme is described in NEC Electronics Inc.'s uPD75104/75106 Application Note 11, April 1987. The approach described in NEC's application note is limited to a maximum of 4800 BPS for the NEC 753XX family of processors. Other approaches to handle asynchronous communications require bit-toggling of the port under program control and place a greater limit on the amount of processing that can be done during communication.
Most asynchronous communications standards and support software for electronic metering require a minimum of 9600 BPS. In addition, with respect to the metering art, it is desirable to avoid limiting, to the extent possible, the amount of processing performed during communications. Moreover, and importantly, saving the utilities the added cost of having to purchase a UART is highly desirable. There is a need, therefore, for a method and apparatus which provides 9600 BPS communication without requiring additional hardware and which does not monopolize microcontroller time so as to avoid limiting registration of energy consumption.